It is estimated that over 5% of the U.S. population over 65 and over 15% of the U.S. population over 85 are affected by Alzheimer's disease. (Cross, A. J., Eur. J. Pharmacol. (1982) 82: 77 -80; Terry, R. D., et al., Ann. Neurol. (1983) 14: 497-506). It is believed that the principal cause of confinement of the elderly in long term care facilities is due to this disease, and approximately 65% of those dying in skilled nursing homes suffer from it.
Certain facts about the biochemical and metabolic phenomena associated with the presence of Alzheimer's disease are known. Two morphological and histopathological changes noted in Alzheimer's disease brains are neuro-fibrillary tangles (NFT) and amyloid deposits. Intraneuronal neurofibrillary tangles are present in other degenerative diseases as well, but the presence of amyloid deposits both in the intraneuronal spaces (neuritic plaques) and in the surrounding microvasculature (vascular plaques) seems to be characteristic of Alzheimer's. Of these, the neuritic plaques seem to be the most prevalent (Price, D. L., et al., Drug Development Research (1985) 5: 59-68). Plaques are also seen in the brains of aged Down's Syndrome patients who develop Alzheimer's disease.
Plaque-rich brains of Alzheimer's patients have been used as a source to extract an approximately 4.2 kd "core" polypeptide, amyloid plaque core protein (APCP). This peptide was designated .beta.-protein by (Glenner, G., et al., Biochem. Biophys. Res. Commun. (1984) 120: 885-890). The amino acid sequence of the amino-terminus was determined (Glenner, G., et al., Biochem. Biophys. Res. Commun. (1984) 122: 1131-1135; Masters, C. L., et al., Proc. Natl. Acad. Sci USA (1985) 82: 4245-42259). The amino acid sequences reported by the two groups were identical, except that Glenner et al. reported a glutamine residue at position 11 for Alzheimer's disease cerebral vascular amyloid whereas Master et al. reported glutamic acid at position 11. Also, the former authors reported that the cerebral vascular amyloid has a homogeneous amino-terminus, while the latter authors reported heterogeneous amino-termini. Both groups showed that the same peptide is found in the amyloid plaque cores and vascular amyloid of adult Down's syndrome-afflicted individuals and report glutamic acid at position 11. Wong, C. W., et al. (Proc. Natl. Acad. Sci. USA (1985) 82: 8729-8732) showed that a synthetic peptide which was homologous to the first ten amino acids of the .beta.-amyloid core protein described by Masters (supra) was able to raise antibodies in mice and that these antibodies could be used to stain not only amyloid-laden cerebral vessels, but also neuritic plaques. These results were confirmed by Allsop, D. et al., Neuroscience Letters (1986) 68: 252-256 using antibodies directed against a synthetic peptide corresponding to amino acids 8-17. Thus, in general, the plaque protein found in various locations of the brain of Alzheimer's patients appears to be similar in immuno-reactivity. It is highly insoluble, as shown by the inability to achieve solubilization in many commonly used denaturants, such as detergents and chaotropic agents (Masters, supra, Allsop, D., et al. (supra)).
There are six known instances of disease-associated amyloid deposits in which the amyloid is produced from a precursor protein: for primary amyloidosis, the precursor is an immunoglobulin light chain; for secondary amyloidosis, the precursor is amyloid A protein; for amyloidosis, prealbumin or a variant thereof; for medullary carcinoma of thyroid, a procalcitonin fragment; and for hereditary cerebral hemorrhage, gamma-trace fragment (See, e.g., Glenner, G. New England Journal of Medicine (1980.) 302: 1283; Sletton, K., et al. Biochem J (1981) 195: 561; Benditt, et al. FEBS Lett(1971) 19:169; Sletton, K., al., Eur J Biochem (1974) 41: 117; Sletton, K. J Exp Med (1976) 143: 993). The foregoing is a partial list and there are at least a number of additional references with regard to procalcitonin fragment as a precursor for the amyloid of the thyroid carcinoma.
It is believed, by analogy to other known instances of disease-associated amyloid deposits, that the .beta.-amyloid core protein associated with Alzheimer's disease is formed from a precursor protein. A protein containing the .beta.-amyloid core protein sequence within the framework of a larger protein was described by Kang, J., et al., (Nature (1987) 325: 733-736). The sequence of this protein was deduced from the sequence of a cDNA clone isolated from a human fetal brain tissue cDNA library and consists of 695 amino acid residues wherein the amino terminus of the .beta.-amyloid core protein begins at position 597. A second precursor protein containing the .beta.-amyloid sequence was predicted from a cDNA clone isolated by Ponte, et al. (Nature (1988) 331: 525-527). The cDNA clone isolated by Ponte et al. encoded a precursor protein which is identical to that identified by Kang, et al., except that it contains an additional 57-amino acid sequence inserted upstream of the .beta.-amyloid core protein sequence. The 57-amino acid insert sequence comprises a functional domain which is highly homologous to a series of protease inhibitors known as the Kunitz-type serine protease inhibitors. Others have characterized an additional amyloid precursor protein (See Kitaguchi, et al., Nature (1988) 331: 530-532) which contains 770 amino acids. The precursor identified by Kitaguchi is identical to that of Ponte et al., except that it contains an additional 19 amino acids adjacent the 57-amino acid protease inhibitor domain. It is not known that these additional 19 amino acids provide any additional functionality to the molecule. The various amyloid precursor proteins which have been identified from cDNA clones arise as the result of alternative message splicing during transcription of a single amyloid precursor gene.
It has been shown that the amyloid precursor proteins are processed by normal cellular metabolism to produce the .beta.-amyloid core protein (Haass, et al. Nature (1992) 359: 322-325; Shoji, et al. Science (1992) 258: 126-129,; Seubert, et al. Nature (1992) 359: 325-327). It is unclear, however, if individuals with Alzheimer's disease produce higher amounts of the .beta.-amyloid core protein, although it has been shown that individuals with Down's syndrome, who invariably develop Alzheimer's disease, express two-fold more B-amyloid precursor protein (Neve, et al. Neuron (1988) 1: 669-677). It is believed that the development of amyloid plaques in Alzheimer's disease brains results from excess production and/or reduced clearance or sequestration of the .beta.-amyloid protein. Hence, if means could be devised for intervening in the process of plaque formation by preventing or inhibiting the processing of the precursor to produce the amyloid plaque core protein, such means could constitute a method of treating or ameliorating the progression of Alzheimer's disease. Until now, however, the processing of amyloid precursor protein to produce the .beta.-amyloid core protein has not been sufficiently understood to allow for effective therapeutic intervention in the process which results in amyloid deposition.
Numerous reports exist describing putative proteinases which are purported to be responsible for generating the .beta.-amyloid protein and/or Alzheimer's disease pathology. These putative proteinases include a broad spectrum of classes of enzymes, for example, serine, cysteine, and metallo-proteinases. A number of .beta.-amyloid forming proteinases have been isolated and characterized. Some reported candidates include multicatalytic proteinase (FEBS 304: 57-60 (1992) and FEBS Lett. 257: 388-92 (1989)), mast cell chymase (J. Biol. Chem. 265: 3836-43 (1990), metallo-endopeptidase 24.15, Biochem. Biophys. Res. Commun. 185: 746-52 (1992)), calcium-activated neutral proteinases (calpain) (J. Neurosci.) 10: 2400-11 (1990), a calcium-activated serine proteinase (Biochem. Biophys. Res. Commun. 174: 790-96 (1991)), and prolyl-endopeptidase (FEBS Lett. 160: 131-34 (1990)). The physiological relevance for each of these candidate .beta.-amyloid forming proteinases has not been demonstrated, for example, by concomitant inhibition of enzymatic activity with blocked .beta.-amyloid protein formation.
Many proteinases have been reported as being altered in Alzheimer's disease brain tissue. For example, .alpha.-1-trypsin-like immunoreactivity has been shown to be increased in Alzheimer's disease brain (Biochem. Biophys. Res. Comm. Vol. 193(2): 579-84 (1993)), three different metalloproteinases have been reported as elevated in Alzheimer's disease brain (J. Neurochem. Vol. 58: 983-92 (1992)), multicatalytic proteinase alterations have been observed (Neurosc. Res. Comm, Vol. 8(3): 185-90 (1991)), abnormal cathepsin D and B immunoreactivity has been reported (Neurosc. Lett. 130: 195-98 (1991) and Proc. Natl. Acad. Sci. 87: 3861-65 (1990)), and calcium-activated neutral proteinase (calpain) has been variously shown to be decreased (Neurobio. of Aging, 11: 425-31 (1990)), increased (Proc. Natl. Acad. Sci. USA 90: 2628-32 (1993)), or to be unaltered (J. Neurol. Sci, 102: 220-34 (1991)) in Alzheimer's disease brain tissue.
The foregoing demonstrates that, although there has been a tremendous amount of work reported in this area, there is no general consensus as to classes of proteinases which are effective in treating Alzheimer's disease or if these proteinases are altered upon contact with Alzheimer's disease brain tissue.
It is an object of the present invention to provide compounds and pharmaceutical compositions, and methods for inhibiting the production of .beta.-amyloid core protein and the formation of amyloid plaques in an individual suffering from dementia of the Alzheimer's type.
It is a further object of the invention to provide pharmaceutical compositions, and methods for treating or ameliorating the progression of Alzheimer's disease.